Size of emerald ash borer in North Carolina,USA: Preliminary evidence for a sawtooth cline?

Abstract

We test the hypothesis of Marshall et al. (2013) that in the United States there is a converse Bergmann's cline in body size of Agrilus planipennis (emerald ash borer, EAB), with the largest females ( = 12.6 mm length) collected at the most southern latitudes tested (37° N). In 2020, we employed three techniques to collect EAB at a North Carolina (NC) site located at 35.64° N (purple prism traps [PPTs], log emergence, Cerceris fumipennis biosurveillance). The study was repeated in 2021, but with green funnel traps replacing log emergence. EAB collected by C. fumipennis in three altitudinally disparate regions of NC were also measured. Overall, EAB collected in 2020 averaged 12.02 mm, with those emerged from logs significantly smaller than those from PPTs. Length of females collected from C. fumipennis at three elevations was not significantly different and averaged 12.01 mm. In 2021, females collected from funnel traps, PPTs and C. fumipennis were not significantly different and larger ( = 12.41 mm) than in 2020; eliminating the smaller log‐emerged EAB from the 2020 data set did not change the outcome. Mean EAB size in NC never reached the reported 12.6 mm at 37° N, regardless of the technique or altitude tested. Our expansion of the latitudinal range in which EAB body size has been studied may shift the proposed converse Bergmann's cline to that of a sawtooth or other non‐linear model, likely associated with a transition in EAB voltinism at or near NC latitudes.